The present invention relates to friction clutches in general, and more particularly to improvements in friction clutches of the type wherein one or more pressure plates can be biased axially by a diaphragm spring. Still more particularly, the invention relates to improvements in friction clutches of the type wherein the diaphragm spring is tiltable or pivotable between two annular seats which are carried by a cover and wherein the pressure plate is engaged by that (outer) marginal portion of the diaphragm spring which extends radially outwardly beyond the seats. The means for engaging or disengaging a friction clutch of such character can comprise an actuating device in the form of a release bearing which can tilt the diaphragm spring between the seats by acting upon the tips of prongs which form part of the diaphragm spring and extend radially inwardly of the seats.
A friction clutch of the above outlined character is disclosed, for example, in commonly owned German Offenlegungsschrift No. 2,911,723. The diaphragm spring which is used in the friction clutch of this German publication resembles a hollow conical frustum having a circumferentially complete outer marginal portion and an annulus of radially inwardly extending prongs whose tips surround a centrally located opening and which are separated from one another by elongated radially extending slots having enlarged outer portions in the form of holes forming an annulus which is inwardly adjacent the marginal portion. The enlarged outer portions of the slots can have a substantially circular, elliptical or other outline.
A drawback of heretofore known diaphragm springs and of friction clutches which employ such diaphragm springs is that the magnitude of torque which can be transmitted is limited or can be increased only by departing from the optimal design and/or dimensions of the friction clutch.